Heat-sensitive recording mediums (materials) which utilize a reaction between a dye precursor and a developer and obtain a colored image by reacting both substances by means of thermal energy are well known. Such heat-sensitive recording mediums are relatively inexpensive. And also, recording apparatuses are compact and easy to maintain. Therefore heat-sensitive recording materials are used not only as recording mediums for fax machines and/or printers, but also for a wide range of fields.
However, the required performance and quality of the heat-sensitive recording materials have been diversified in step with the expansion of applications. Therefore, for example, heat-sensitive recording mediums require an increased optical density, image stabilization, and a metallic color tone. Furthermore, a multicolor heat-sensitive recording medium which has not only a single color tone but rather a multicolor tones, wherein the each color is developed at high optical density, and a recording part (developed image) has excellent color separation properties, is required.
Further, a two-color heat-sensitive recording medium having a color tone tinged with a metallic luster such as a gold metallic tone as one of the colors can further accentuate text or graphics by taking advantage of conventionally unavailable color combinations, so there is a high demand for practical applications.
In particular, with regard to heat-sensitive recording mediums in which a colored image has a metallic color tone, whose range of application has the potential to expand, it has been proposed to form a coating layer containing a pigment, which is prepared by coating the surface of natural mica with at least one type of titanium oxide and/or iron oxide, on a heat-sensitive recording layer (see Patent Document 1) or to form a layer containing an inorganic pearl pigment on a heat-sensitive recording layer (see Patent Document 2). But such efforts have not necessarily reached the satisfied results with regard to the metallic tone, optical density, and/or image stability.
Further, a two-color heat-sensitive recording medium having a yellow color tone can further accentuate text or graphics by taking advantage of a vivid yellow color tone, so there is a high demand for practical applications.
As a multicolor heat-sensitive recording medium having a yellow color tone, it has been proposed that only a low-temperature coloring layer is developed by a low-temperature developing operation, and at the time of a high-temperature developing operation, a decolorizing agent having a decolorizing effect acts on the coloring system of the low-temperature coloring layer so as to achieve developing of only a high-temperature coloring layer (see Patent Documents 3 to 5), and that two distinguishable colors are developed by laminating two heat-sensitive recording layers which are developed in different color tones and which are provided different amounts of heat (see Patent Document 6). But such efforts have not necessarily reached the satisfied results with regard to color separation properties, optical density, and/or image stability.